It is common practice in the control of locomotive traction motors to provide protection systems for interrupting the motor voltage supply upon the detection of a ground fault or flashover in the motor. In some systems, the reconnection of motor voltage is manually initiated by the operator; in other systems, the reconnection is automatically initiated after a predetermined time interval of interruption. In either type of system, the motor voltage supply is (or should be) permanently interrupted in the event of repeated ground faulting or flashover indicative of a so-called hard failure. In such event, the affected motor should be serviced before operation is resumed.
A disadvantage of protective systems of the above type is that ground faulting caused by an accumulation of moisture on the traction motor windings can result in permanent interruption of the motor voltage. As a result, the motor is effectively disabled until the moisture dries.